Total solar eclipse to create narrow dark path across U.S.

A total eclipse of the sun will turn day into night across a narrow swath of the U.S. this month when the full moon moves to block the sun’s face and create a coast-to-coast phenomenon that hasn’t occurred in nearly 130 years.

Millions of people in 12 states will be watching on Monday, Aug. 21, as the eclipse crosses 1,800 miles from the Oregon coast to South Carolina, creating a band of darkness on the ground roughly 70 miles wide. Only the sun’s corona will be visible as a fiery halo of blazing gas.

The path of the total eclipse will start near the coastal Oregon town of Lincoln Beach at 10:16 a.m. PDT. Then it will move across the state and on to Idaho, on to Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennessee, North Carolina and Georgia before heading out to sea near Charleston, S.C., at 2:48 p.m. EDT. Its path will also cross over tiny uninhabited patches of Montana and Iowa, but only for a few seconds.

In the Bay Area, watchers will see a brilliant partial eclipse. The moon will take its first bite of the sun’s edge at 9:01 a.m. PDT. By 10:15 a.m., 76 percent of the sun will be blocked, dimming daylight as if it were somewhat cloudy. The eclipse here will end at 11:37 a.m.

Libraries, colleges and science institutions like the California Academy of Sciences, the Exploratorium and UC Berkeley’s Lawrence Hall of Science are offering public programs and apps that explain the eclipse. During totality, many will air the celestial event online in real time from the telescopes of astronomers across the country.

More on Solar Eclipse

“It’s the first eclipse of the Internet age,” said Andrew Fraknoi, former chairman of astronomy at Foothill College in Los Altos. He estimates that more than 450 million people from Canada to Mexico will watch at least part of the event.

But Fraknoi has an important warning for anyone who plans to watch any part of it. “The sun’s visible and invisible rays can cause serious damage to the sensitive tissues of the eyes,” he said. “Looking directly at even part of an eclipse can be extremely dangerous, and a glimpse of its light before totality can blind you. Protection is essential.”

The best way to watch the eclipse is to use full eye protection like specially approved eclipse glasses or No. 13-rated or better welder’s glass, Fraknoi said.

Those who don’t have access to the right kind of protective glasses can make or buy pinhole projectors. An ordinary kitchen colander can also do the trick. Held overhead with its bowl turned up, a colander’s holes can turn the sunlight into a spangle of eclipse images on the ground.

Even a leafy tree can become a solar image projector, Fraknoi said.

Total eclipses of the sun are by no means rare — at least one occurs somewhere on Earth every 18 months or so, but the U.S. won’t see another total eclipse until April 8, 2024, when it will be visible along a path from Texas to Maine.

This month’s cross-country eclipse will be a phenomenon not seen since 1889. Where the eclipse is total, daylight will turn to midnight as the moon briefly covers the sun’s face. The summer air will turn chilly, birds will chirp uneasily in the unexpected darkness, and the stars will emerge.

Totality times for many eclipses can vary widely and some have lasted seven minutes or more, but astronomers calculate that this eclipse will at most last two minutes, 40.6 seconds before the moon moves on.

David Perlman became the San Francisco Chronicle's science editor emeritus in August of 2017. Perlman previously served as The Chronicle's veteran science editor, reporting on research and scientific advances at California universities and research centers. He has also reported from many places around America from Cape Canaveral to Alaska, and around the world from Antarctica to the Galapagos Islands and from China to Ethiopia. He is a past president of the National Association of Science Writers and the Council for the Advancement of Science Writing and is a Fellow of the California Academy of Sciences.